It is half-way down the small intestine between its duodenum and ileum sections.
The term "jejunum" derives from the Latin jejunus, "empty of food, meager", or "hungry". The ancient Greeks noticed at death that this part of the intestine was always empty of food; therefore, the name, jejunum.
The Latin jejunus also gave rise to jejune, "lacking in nutritive value and devoid of substance, significance," or "interest"; and "that which is dull". A "jejune argument" is one which is empty (like the jejunum) and totally devoid of interest.